This invention relates generally to rockdrills. More particularly the invention relates to an on-off valve for a hydraulic rockdrill which is operable by a hydraulic fluid under pressure and which is controlled by a hydraulically biassed valve.
Presently known hydraulic handheld rockdrills typically use a throttle valve for on and off and power regulating functions. The throttle valve is adjusted by the operator by turning a lever that opens and closes a port supplying fluid to the drill. Because the throttle valve port carries all the flow which powers the drill it must be fairly large, usually in the order of 7/16 to 1/2 inch to 11.11 to 12.7 mm) in diameter. When operating at high pressure, as most hydraulic drills do, the handle torque required to operate the valve becomes excessive making the handle difficult to turn. This is primarily due to friction created by the large force imbalance across the valve port. Due to the stiffness of the handle, many operators often do not turn the drill off between holes and thus accumulate unproductive running time on drill cmponents. Additionally, the complexity and number of parts associated with a throttle valve assembly add cost and decrease the reliability of a rockdrill.
The foregoing illustrates limitations known to exist in present handheld hydraulic rockdrills. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.